New floor construction, what would be recommended?

Thanks first of all for the many informations. I know that the reasonable solution would be a screed with screed boards and other stuff etc. But what worries me is simply the height of about 40mm which I would like to keep so that the hallway does not become significantly higher than the rooms. And a proper solution would certainly be a few cm higher? The base is the concrete slab. On top of it I now wanted to lay 6mm laminate plus 2mm impact sound insulation. That would make the new floor a few mm higher than before anyway, which is still within limits. With about 7sqm this hallway is not particularly large and does not have any special loads. It will only be walked over briefly to change rooms.

On a concrete slab everything is much easier because it is load-bearing. So leveling and fiber cement boards. But since it is obviously the floor slab, there should already be thermal insulation. In these areas I use rigid foam boards that are aluminum-faced. They come in different thicknesses.

But since it is obviously the floor slab, there should already be thermal insulation.

Just as a note, an excerpt from the original post: "In our old building in the hallway of the attic, I noticed ..." That on the subject of "obvious floor slab"!

Just as a note, an excerpt from the original post:
"In our old building in the attic hallway I noticed ..."
That regarding the topic "obvious concrete slab"!

Does old building mean that the floor consists of wooden beams? I don’t know the exact definition. For me, old building is everything that is already relatively old. Yes, concrete ceiling. How exactly it is I just don’t know. But 40mm is certainly too little to do a leveling, impact sound insulation and concrete slab etc. here? Or put differently, what would be the minimum height needed to do something like that properly?

Just as a note, an excerpt from the original post:
"In our old building in the hallway attic floor, I noticed ..."
That on the topic of "obvious floor slab"!

That happens to me more often with age, thanks!

Does "Altbau" mean that the floor is made of wooden beams? I don’t know the exact definition. For me, Altbau is anything that is already relatively old. Yes, concrete ceiling. I just don’t know how this one is exactly. But 40mm is certainly too little to make a leveling, impact sound insulation, and subfloor here? Or to put it differently, what would be the minimum height needed to do something like this properly?

Residential and commercial buildings are classified as "Altbauten" starting from 25 (usable) years. And 40mm is indeed tight as a maximum height for the entire buildup. Under consideration of the necessary load distribution layer (e.g., wood chipboard), it will hardly be possible to install impact sound insulation that deserves its name within a maximum of 40mm. With gypsum fiber boards, e.g., KNAUF Brio, the substrate must be even. So, a surface leveling on the raw ceiling including mechanical substrate preparation would be added here. However, a special solution would be possible! Although clients usually shy away from spending the money on it (which I do not assume here). Keyword: "Turbolight(R) system." With this, I had almost 5,000m² of a no longer fully load-bearing ceiling construction renovated in Berlin in a highly frequented commercial area. And it works!